A prospective evaluation of selection criteria for the use of Nucleic Acid Amplification Techniques to test for the presence of Mycobacterium tuberculosis in respiratory tract samples.

Background: Although Mycobacterium tuberculosis (MTB) can be detected rapidly by means of Nucleic Acid Amplification Techniques (NAT), these NAT tests are expensive and therefore are not used in routine practice or as a screening tool. Methods: Although it is generally accepted that clinical and radiological data are important markers for deciding whether to test for MTB using NAT, the optimal combination of markers has not been determined. A prospective study was performed to evaluate NAT using different combinations of clinical, laboratory and radiographic selection criteria. Results: The sensitivity of NAT for detecting MTB in patients with smear negative for acid-fast bacilli was two times higher in patients with radiographic abnormalities and negative routine bacterial culture for respiratory pathogens than those with absence of radiographic abnormalities or positive routine bacterial culture (77.8%, vs. 33.3%; p < 0.001). Furthermore, a difference of almost 40% can be observed between the positive predictive values of both groups (87.5%. vs. 50.0%,; p < 0.001). Conclusions: Using a combination of clinical, laboratory and radiographic criteria, it is possible to identify patients in whom the NAT for MTB has reasonable sensitivity and specificity. Using these selection criteria should reduce costs associated with the inappropriate use of NAT tests. (Clin. Lab. 2009;55:441-446)